My fiance and I are working on putting together a christmas CD. I play guitar and she plays trumpet. We have been arguing over the notes that she is playing on the trumpet. She says that her tuning note is a C, however, on the tuner it is coming up as a Bb.

I thought that maybe the tuner wasn`t working right, but when I play a Bb on the guitar with her tuning note, they match. I tuned my guitar to 2 different tuners to make sure my notes were correct too. So I am 100% confident that the note coming out of the trumpet is a Bb not a C.

Well this made her pretty mad. So we had a nice little fight about it. That was not very fun.

We tried playing with her tuning slide a whole bunch and we couldn`t get it up to a C. Then we played with some other slides and that threw it way out of whack.

So here are my questions.
Is there something wrong with her trumpet?
Should it be playing a C as the tuning note?
What would cause it to be playing a full step lower than what she expects?
Was she taught the wrong notes?

If anyone has some light to shed on the subject, I`d appreciate it. Thanks.

Trumpet is in the key of Bb and the piano is in the key of C.

So tranposition comes into effect her...when she plays her C she is actually playing a Bb in the key of C.

I would look up some music theory things on transposing before going any farther.

I do know that from the Key of C a trumpet is half a step up hence the Bb showing on the tuner when she plays a C on her horn.